We just purchased a Novatel USB551L for connecting our Balance 20 to Verizon Wireless in a failover situation. Initially I could not get the modem to connect. It was only after I upgraded the firmware to the latest version the modem immediately connected.
I probably should have thought of this upfront - but it would be a good idea for the Peplink user manual to call this out. The troubleshooting section doesn’t mention to download the latest firmware as part of any troubleshooting exercise.